EuIII Complexes of Octadentate 1-Hydroxy-2-pyridinones: Stability and Improved Photophysical Performance*

Evan G. Moore; Anthony D’Aléo; Jide Xu; Kenneth N. Raymond

doi:10.1071/CH09314

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Eu^III Complexes of Octadentate 1-Hydroxy-2-pyridinones: Stability and Improved Photophysical Performance*

Evan G. Moore ^A ^B , Anthony D’Aléo ^A ^B , Jide Xu ^A ^B and Kenneth N. Raymond ^A ^B ^C

+ Author Affiliations

- Author Affiliations

^A Chemical Sciences Division, Lawrence Berkeley National Laboratories, 1 Cyclotron Road, Mail Stop 70A1150, Berkeley, CA 94720, USA.

^B Department of Chemistry, University of California, Berkeley, CA 94720, USA.

^C Corresponding author. Email: raymond@socrates.berkeley.edu

Australian Journal of Chemistry 62(10) 1300-1307 https://doi.org/10.1071/CH09314
Submitted: 2 June 2009 Accepted: 12 September 2009 Published: 13 October 2009

Abstract

The luminescence properties of lanthanoid ions can be dramatically enhanced by coupling them to antenna ligands that absorb light in the UV-visible and then efficiently transfer the energy to the lanthanoid centre. The synthesis and the complexation of Ln^III cations (Ln = Eu, Gd) for a ligand based on four 1-hydroxy-2-pyridinone (1,2-HOPO) chelators appended to a ligand backbone derived by linking two l-lysine units (3LI-bis-LYS) is described. This octadentate Eu^III complex ([Eu(3LI-bis-LYS-1,2-HOPO)]^–) has been evaluated in terms of its thermodynamic stability, UV-visible absorption and luminescence properties. For this complex, the conditional stability constant (pM) is 19.9, which is an order of magnitude higher than diethylenetriaminepentacetic acid at pH = 7.4. This Eu^III complex also shows an almost two-fold increase in its luminescence quantum yield in aqueous solution (pH = 7.4) when compared with other octadentate ligands. Hence, despite a slight decrease of the molar absorption coefficient, a much higher brightness is obtained for [Eu(3LI-bis-LYS-1,2-HOPO)]^–. This overall improvement was achieved by saturating the coordination sphere of the Eu^III cation, yielding an increased metal-centred efficiency by excluding solvent water molecules from the metal’s inner sphere.

Acknowledgement

This work was partially supported by the National Institutes of Health (NIH) (grant HL69832) and supported by the Director, Office of Science, Office of Basic Energy Sciences, and the Division of Chemical Sciences, Geosciences, and Biosciences of the US Department of Energy at Lawrence Berkeley National Laboratory (LBNL) under Contract no. DE-AC02–05CH11231. This technology is licensed to Lumiphore, Inc. in which some of the authors have a financial interest. Professor Gilles Muller is thanked for access to the low-temperature time-resolved luminescence facilities.

References

^* This paper is dedicated to a giant of Australian chemistry, Alan Sargeson. The senior author had the great good fortune to spend his first sabbatical leave in Australia, much of it at the Australian National University. It left a lasting influence regarding coordination chemistry and its interface to biology and medicine.

EuIII Complexes of Octadentate 1-Hydroxy-2-pyridinones: Stability and Improved Photophysical Performance*

Abstract

Acknowledgement

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Eu^III Complexes of Octadentate 1-Hydroxy-2-pyridinones: Stability and Improved Photophysical Performance*